Signalling channel and radio system for power saving in wireless devices

ABSTRACT

Wireless devices, transmitters, systems and methods are provided that have a narrow band signaling channel and a wide band channel, for example an OFDM channel. In order to save power, the wireless device is nominally powered down with the exception of a receiver specific to the narrow band signaling channel. Once instructed to do so over the narrow band signaling channel, the wireless device wakes up the rest of its wide band receive circuitry.

RELATED APPLICATION

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 13/571,467, filed on Aug. 10, 2012,which is a continuation of, and claims priority to, U.S. Pat. No.8,264,996, filed on Jan. 8, 2010 and issued on Sep. 11, 2012, which is acontinuation of, and claims priority to, U.S. Pat. No. 7,672,258, filedon Sep. 24, 2004 and issued on Mar. 2, 2010, the disclosures of whichare hereby incorporated by reference in their entirety.

BACKGROUND

Power supply management is a significant challenge in terminal and smartsensor design. This is because such terminals and sensors typically havea limited battery capacity. Anything that can be done to reduce powerconsumption for such wireless terminals and sensors would be of benefit.

Traditional terminal/receiver designs drain a large amount of power evenif the terminal is in an idle or dormant mode. The reason for this isthat the terminals are required to monitor a paging channel or a beaconchannel all the time.

OFDM (orthogonal frequency division multiplexing) terminals typicallydrain even more power than CDMA/TDMA (code division multiple access/timedivision multiple access) terminals due to the fact that such terminalsrun their wide band and high resolution ADC (analog-to-digitalconverter) and FFT (Fast Fourier Transform)/sub-FFT engines all thetime, or at least during any period that detection of any signals is tobe possible.

For example, an OFDM terminal in sleep mode will typically periodicallywake up to see if it has any messages. However, conventional terminalsmust perform processing on the full OFDM bandwidth to see if there areany messages. This takes a significant amount of power because a fullanalog-to-digital conversion on the entire bandwidth of the OFDM systemmust be performed together with the processing of the whole digitizeddata block in terms of data buffering, framing, full FFT computationetc. Typically, the paging channel is transmitted at a particular timeand frequency with the same processing engine as the main task channelsand the terminal must wake up in order to look at the paging channel.

It is also noted that due to the high peak-to-average power ratio, theADC needs to cover a high dynamic range, and this also increases thepower consumption.

SUMMARY

At least one embodiment provides a wireless device comprising: a wideband receiver adapted to receive a wide band signal; and a narrow bandreceiver adapted to receive a narrow band signal, and to process thenarrow band signal to determine whether or not to wake up the wide bandreceiver, and to wake up the wide band receiver if so determined.

In some embodiments, the narrow band receiver is a passive device.

In some embodiments, the narrow band receiver is a semi-passive device.

In some embodiments, the wide band receiver is an OFDM receiver.

In some embodiments, the wide band signal comprises an OFDM signal withzeros inserted at sub-carrier location(s) where the narrow band signalis to reside.

In some embodiments, the wireless device comprises a power supply and aswitch connecting the power supply to the wide band receiver undercontrol of the narrow band receiver, wherein waking up the wide bandreceiver comprises controlling the switch to supply power to the wideband receiver.

In some embodiments, processing the narrow band signal to determinewhether or not to wake up the wide band receiver comprises demodulatingand decoding the narrow band signal and checking if the narrow bandsignal has a message for this wireless device or not.

In some embodiments, the wide band receiver is a CDMA receiver and thewide band signal is a CDMA signal.

In some embodiments, the signaling channel occupies a spectrum adjacentto a spectrum of the CDMA signal.

In some embodiments, the narrow band receiver wakes itself up on aperiodic basis.

At least one embodiment provides a transmitter adapted to generate asignal containing a wide band signal and a narrow band signal, whereinthe narrow band signal contains information instructing particularwireless devices to wake up to receive the wide band signal.

In some embodiments, the transmitter comprises: a first IFFT functionhaving a plurality of data inputs, and at least one zero input in afrequency location(s) where the narrow band signal is to reside; asecond IFFT having zero inputs at frequency locations corresponding tothe plurality of data inputs, and at least one signaling channel inputin the frequency location(s) where the narrow band signal is to reside.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least one zero input in a frequencylocation(s) where the narrow band signal is to reside; a narrow bandmodulator for generating the narrow band signal operating at a signalingchannel frequency where the zeros were inserted.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs; a narrow band modulator for generating thenarrow band signal operating at a signaling channel frequency out of anoperating bandwidth of the wide band signal.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least one zero input in a frequencylocation(s) where the narrow band signal is to reside; a narrow bandmodulator for generating the narrow band signal operating at multiplefrequencies.

In some embodiments, the transmitter comprises: an IFFT function havinga plurality of data inputs, and at least signaling channel input in afrequency location(s) where the narrow band signal is to reside.

In some embodiments, the transmitter comprises: a main CDMA signalgenerator operating in a CDMA bandwidth for generating a main CDMAsignal; a signal channel generator operating at an edge of the CDMAbandwidth for generating the narrow band signaling channel.

In some embodiments, the transmitter comprises: a main CDMA signalgenerator operating in a CDMA bandwidth for generating a main CDMAsignal; a signal channel generator operating outside the CDMA bandwidthfor generating the narrow band signaling channel.

At least one embodiment provides a method comprising: communicating awide band signal; and communicating a narrow band signal, the narrowband signal indicating whether or not to wake up a wide band receiver.

In some embodiments, the communicating the wide band signal and thenarrow band signal comprise transmitting these signals.

In some embodiments, the communicating the wide band signal and thenarrow band signal comprises receiving these signals.

In some embodiments, the wide band signal is OFDM signal with zerosinserted at sub-carrier location(s) where the narrow band signal is toreside.

In some embodiments, the method further comprises: examining the narrowband signal to determine whether or not to wake up the wide bandreceiver; waking up the wide band receiver if so determined.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will now be described with reference to the attacheddrawings in which:

FIG. 1 is a frequency plan of an example implementation of a downlinksignaling channel provided by one or more embodiments;

FIG. 2A is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signaling channel according to oneor more embodiments;

FIG. 2B is a block diagram of a transmitter adapted to generate both awide band OFDM signal, and narrow band signaling channel according toone or more embodiments;

FIG. 2C is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signaling channel according one ormore embodiments;

FIG. 2D is a block diagram of a transmitter adapted to generate both awide band OFDM signal and narrow band signaling channel which has centerfrequency at a certain frequency that may not necessarily be locatedinside the OFDM spectrum according to one or more embodiments;

FIG. 3 is a block diagram of a wireless device adapted to receive anarrow band signaling channel in accordance with one or moreembodiments;

FIG. 4 is a block diagram of another wireless device adapted to receivea narrow band signaling channel in accordance with one or moreembodiments;

FIG. 5 is a block diagram of a CDMA transmitter that is adapted togenerate a narrow band signaling channel in accordance with one or moreembodiments; and

FIG. 6 is an example of spectrum utilization for a UMTS wireless deviceadapted to receive a narrow band signaling channel in accordance withone or more embodiments.

DETAILED DESCRIPTION

In order to reduce the power consumption of a wireless device due to theprocessing of the received paging channel or similar channels, a newsignaling channel is provided for use in OFDM systems. The bandwidth ofone or more tones or pieces of spectrum are pre-assigned at a certainfrequency or frequencies. One of the tones or one piece of spectrum ortheir combinations is used for signaling. The new signaling channelmight contain beacon channel information or paging channel informationor system information to name a few examples. The total bandwidth ofthis particular channel can be selected depending upon the designatednetwork capacity. In some embodiments, this channel information ismodulated in the time domain, for example as a PSK (phase shift keying)signal or as an AM signal or otherwise. In another embodiment, thechannel information is modulated in the frequency domain similar toOFDM. In some embodiments, the signaling channel is encoded andmodulated separately from the remaining of the OFDM transmission andtherefore the paging channel can be implemented as a separate module tohook up to a primary radio responsible for the generation of the fullOFDM signal, and sometimes with constant modulation. The OFDMsub-carriers are zeroed out if the signaling channel is designed withinband. In other embodiments, the signaling channel can be implementedtogether with the OFDM transmitter. The portion of the transmitterresponsible for generation of the full transmit signal will be referredto as the primary transmitter.

Referring now to FIG. 1, shown is an example of the downlink signalingchannel. Generally indicated at 10 is the typical occupied OFDMspectrum. It can be seen that this consists of a contiguous set ofsub-carriers. The number of sub-carriers will vary for differentapplications. According to at least one embodiment, a portion of thespectrum is reserved, referred to as the reserved spectrum 12. Thereserved subcarriers can be anywhere inside the spectrum 10. Within thisspectrum, there is transmitted a signal which occupies an occupiedsignaling channel spectrum as indicated at 14. The occupied signalingchannel spectrum is designed so as to fall completely within thereserved spectrum 12.

In some cases, the signaling channel bandwidth is an integer multiple ofthe sub-carrier bandwidth.

Referring now to FIG. 2A, shown is a block diagram of a first example ofan OFDM transmitter capable of generating a narrow band signalingchannel in accordance with one or more embodiments. The signalingchannel in this example is implemented in the frequency domain by theprimary transmitter. Shown is an IFFT function 60 having eight inputsconsisting of six data inputs 62 and two signaling channel inputs 64.The IFFT produces a time domain output which is input to aparallel-to-serial converter 66 to produce an overall output 68. In thiscase, a single IFFT 60 is employed to produce the overall outputcontaining both the wide band content and the signaling channel content.In this example and the examples that follow, it is to be understoodthat the number of sub-carriers and the particular location of thesub-carriers for data and signaling are particular to these examples,but that more generally any number of sub-carriers can be employed for awide band content, and the narrow band signaling channel can be insertedanywhere within the wide band spectrum. At times, however, the signalingchannel is inserted at the edge of the available spectrum, and occupiesas few sub-carriers as possible to control the system overhead.

Referring to FIG. 2B, shown is another example of a transmitter adaptedto produce a signal containing both the wide band output and thesignaling channel. In this case, the signaling channel is implemented inthe frequency domain separately from the primary transmitter. Shown is afirst IFFT function 70 receiving as input data inputs 72, and zeroinputs 74 in the frequency locations where the signaling channel is toreside. The output of IFFT 70 is converted to serial form withparallel-to-serial converter 76 to produce a wide band time domainoutput 78. Similarly, a second IFFT function 80 is shown having zeroinputs 82 where the wide band data content is to be located, and havingsignaling channel inputs 84 at the frequency locations where thesignaling channel is to reside. The IFFT 80 produces a time domainoutput which is converted to serial form with parallel-to-serialconverter 86 to produce a signaling channel time domain output 88. Thetwo time domain outputs 78,88 are combined at 90 to produce an overalloutput 92.

A third example of a transmitter for generating an overall outputcontaining the OFDM signal and narrow band signaling channel is shown inFIG. 2C. In this example, the signaling channel is separately designedwithin the reserved spectrum and may or may not involve IFFTfunctionality. In this case the OFDM functionality for the wide bandsignal is the same as that of FIG. 2B, and a wide band time domainoutput is produced at 78. Also shown is a narrow band modulator 96operating at signaling channel frequency. This takes signaling channelinformation 94, modulates it at the signaling channel frequency toproduce the signaling channel output 98 which is combined at 100 withthe wide band time domain output 78 to produce an overall output 102.

A fourth example of a transmitter for generating an overall outputcontaining the OFDM signal and narrow band signaling channel is shown inFIG. 2D. In this case, the OFDM functionality for the wide band signalis the same as that of FIG. 2B, and a wide band time domain output isproduced from data inputs 95 at 78. Also shown is a narrow bandmodulator 99 operating at a certain signaling channel frequency. Thistakes signaling channel information 97, modulates it at the signalingchannel frequency to produce the signaling channel output 93 which isseparately transmitted and of course time synchronized with the primarytransmitter. Depending on the frequency location of the narrow bandchannel, it may or may not be necessary to insert zeros for one or moresub-carriers of the OFDM signal. This signaling channel may or may notshare hardware such as RF front end, antenna, etc. with the rest of thetransmitter.

Four very specific examples of OFDM modulation have been shown in FIGS.2A, 2B, 2C and 2D. Of course a transmitter would typically include farmore functions than those shown in these figures. The minimum detailsnecessary to illustrate how the signaling channel can be modulated havebeen included. Also, it is to be understood that the IFFT is but oneexample of a function for generating an OFDM signal.

Referring now to FIG. 3, shown is a block diagram of a wireless deviceprovided by one or more embodiments. The terminal features a wide bandreceiver 16 and a narrow band receiver 18. Also shown is antennafunctionality generally indicated by 20. The antenna functionality mayconsist of a single or multiple antennas connected to both of thereceiver 16 and 18, or may consist of respective antennas connected toeach of the receivers 16 and 18. The narrow band receiver 18 operates toreceive a narrow band signaling channel, and to decide on the basis ofthe narrow band signaling channel whether or not to generate a wake upsignal 22 to wake up the wide band receiver 16. This wake up signal cancome in any appropriate form. For example it might simply be a signal toswitch on a power supply driving the wide band receiver 16. The signalmay contain scheduling information. Once the wide band receiver is on,it will stay on until it is deemed acceptable to power down again. Thismay occur for example after the completion of a transmission of a datapackage after which the wireless device will power down and wait foranother wake-up.

Referring now to FIG. 4, shown is a block diagram of an example wirelessdevice adapted to process both the regular OFDM channel and thesignaling channel, as provided by one or more embodiments. Shown areonly some of the key conventional components of an OFDM receiver forillustration purposes, these consisting of a receive antenna 20, receiveduplexer filter 22, RF receiver 24, analog base-band processor 26. Thereis a power management module 36 connected to both the RF receiver 24 andthe analog base-band processor 26. The analog base-band processor 26 andthe power management module 36 are also both connected to a DSP (digitalsignal processor) microprocessor 28. The DSP microprocessor 28 isconnected to memory 30 which might be flash memory, ROM or SRAM to namea few examples. It is also connected to a display 32 and keypad 34.Finally, there is shown a SIM card 42 having an IP address. Thecomponents described thus far all form part of an example of aconventional OFDM receiver. More generally, any set of functionalitythat is capable of performing normal reception of OFDM signals iscontemplated in place of the above described functionality.

In addition to the conventional receiver, there is a narrow bandreceiver 38 also shown connected to the antenna 20 via filter 22. Thenarrow band receiver is connected to a module where a subscriberidentifier, network information, etc. are stored, for example a SIMcard.

Also shown is a battery 40. Battery 40 is connectable to the powermanagement module or not 36 by power switch 37 depending on instructionsfrom the narrow band receiver 38.

The arrow 39 from narrow band receiver 38 to power switch 37 representsan instruction arrow rather than wiring connection. The dotted arrowfrom battery 40 to narrowband receiver 38 is an optional real connectionfrom which the narrowband receiver may drain power for housekeepingpurposes and internal clock purposes etc. The narrow band receiver mayalternatively have its own battery for housekeeping that is separatefrom the main battery. The narrow band receiver 38 is designed to onlylook at the signaling channel. This can be done in a much more powerefficient manner than would be the case in receiving a paging channelusing all of the conventional receiver circuitry.

In some embodiments, the narrow band receiver 38 is on constantly and iscapable of receiving a message at any time. In another embodiment, thenarrow band receiver 38 wakes itself up on a periodic/scheduled basis.This may for example be achieved by running an internal clock parasiteon the primary radio clock such that after system synchronization, thenarrow band receiver knows when and where the paging channel appears.This latter approach is more power efficient. Once the narrow bandreceiver 38 receives a message for the particular terminal, it will thenwake up the remainder of the wireless device by switching power switch37 over to the power management module 36 such that the terminal is thenoperating in a conventional manner over the entire OFDM spectrum.

In some embodiments, the narrow band receiver 38 does not operate whenthe remainder of the wireless devices are operating in wide bandreceiving mode. In another embodiment, the narrow band receiver 38continues to receive power and to operate even while the remainder ofthe wireless device is powered on.

Not shown in FIG. 4 is all of the circuitry involved for wide-bandtransmission. In duplex implementations, such circuitry would beincluded. However, for the signaling channel, there is only receivefunctionality.

In some embodiments, this new narrow band channel is a replacement foran existing paging channel within the wide-band spectrum. Alternatively,the new signaling channel is used as described, but the existing channelcan also be used to communicate to terminals that are fully powered. Insome embodiments, the narrow band receiver is completely passive, anddoes not require any power supply whatsoever. Examples of receivers thatwould be capable of functioning in this manner are MEMS resonators, MEMSRF receivers, or circuits that are capable of collecting RF energy fromtransmitters via inductive coupling circuitry. All the receiver needs tobe able to do is to receive and process enough of the signal to identifyif there is a message for the particular wireless device.

In other embodiments, the narrow band receiver is semi-passive, having asmall power supply for housekeeping purposes or obtaining a small amountof power from the main power supply. In such an embodiment, power issupplied from the battery for housekeeping purposes. However, there isstill passive circuitry for collecting RF energy that is then used toprocess the paging channel and to turn on/off the power for the mainradio. FIG. 4 shows a passive power source 33 that might be used inpassive or semi-passive implementations.

Referring now to FIG. 5, shown is a block diagram of another transmitterin accordance with at least one embodiment. This embodiment isparticular to CDMA signals. Shown is a main CDMA signal generator 110that generates a wide band CDMA signal 114. Also shown is a signalingchannel generator operating at the edge of the CDMA bandwidth 112 thatproduces a signaling channel output 116. This is combined with the wideband signal 114 at 118, and the sum 119 is up converted at 120 toproduce an overall output 122. The corresponding receiver is similar tothat of FIG. 3 or 4, but with the wide band receiver being a CDMAreceiver.

FIG. 6 shows an example of spectrum utilization for the embodiment ofFIG. 5 specific to a 3GPP/UMTS wireless device. Such wireless devicesemploy signals occupying a 5 MHz bandwidth. The original chip rate forthis standard was 4.096 MCPS (mega chips per second). However, due to achange in the standard now the chip rate is 3.84 MCPS. This results inan amount of extra bandwidth equal to 4.096−3.84=256 kHz. This is enoughfor two narrow band channels with a 128 kHz bandwidth each. This isshown in FIG. 6 where the UMTS signal bandwidth is generally indicatedat 50, and the leftover bandwidth at 52 is now used for narrow bandsignaling channels as described above.

Numerous modifications the various embodiments are possible in light ofthe above teachings. It is therefore to be understood that within thescope of the appended claims, that some embodiments may be practicedotherwise than as specifically described herein.

The invention claimed is:
 1. A method comprising: maintaining a widebandreceiver in a non-processing and power saving mode, where when awakened,the wideband receiver consumes a greater amount of power for processingplural signals obtained from a corresponding plurality of subcarriersdistributed over a pre-specified wide frequency band than when in itsnon-processing and power saving mode; receiving, using an associatednarrow band receiver, a narrow band signal that is transmitted only in anarrow band adjacent to an edge one of the subcarriers, the narrow bandbeing substantially narrower than the pre-specified wide frequency band,the narrow band signal comprising an indication usable to determinewhether or not to wake up the wideband receiver for a case where thatwideband receiver is in its non-processing and power saving mode;processing the received narrow band signal to determine whether to wakeup the wideband receiver based, at least in part, on the indication; andresponsive to determining to wake up the wideband receiver, waking upthe wideband receiver out of the non-processing and power saving mode soas to thereby enable the awakened wideband receiver to process pluralsignals of corresponding plural subcarriers of the wide frequency band,wherein the narrow band signal is located at one of: an edge portion ofthe wide frequency band; or immediately adjacent to but outside of thewide frequency band.
 2. The method of claim 1, wherein the narrow bandsignal further comprises a message for a particular one among aplurality of wireless devices.
 3. The method of claim 1 furthercomprising: periodically waking up the narrow band receiver from anautomatically entered into sleep mode thereof to determine if a nextreceived message within a correspondingly received narrow band signal isone directed to a corresponding wideband receiver associated with thenarrow band receiver.
 4. The method of claim 1, wherein the plurality ofsubcarriers distributed over a pre-specified wide frequency band definean Orthogonal Frequency Division Multiplexing (OFDM) signal.
 5. Themethod of claim 1, wherein waking up the wideband receiver furthercomprises controlling a power supply associated with the widebandreceiver.
 6. The method of claim 1, wherein the narrow band signalcomprises scheduling information associated with the wideband receiver.7. The method of claim 1 further comprising: stopping operation of thenarrow band receiver while the wideband receiver is operating.
 8. One ormore processor-readable memory devices comprising processor-executableinstructions which, responsive to execution by at least one processor,are configured to enable a machine system to: maintain in anon-processing and power saving mode, a wideband receiver that whenawakened consumes a greater amount of power for processing signalsoccupying a pre-specified wide frequency band; receive, using anassociated narrow band receiver, a narrow band signal that istransmitted in a narrow band adjacent to an edge portion of the, andthat is substantially narrower than the pre-specified wide frequencyband, the narrow band signal comprising an indication of whether or notto wake up the wideband receiver for a case where that wideband receiveris in its non-processing and power saving mode; process the narrow bandsignal to determine whether to wake up the wideband receiver based, atleast in part, on the indication; and responsive to determining to wakeup the wideband receiver, wake up the wideband receiver out of thenon-processing and power saving mode so as to thereby enable theawakened wideband receiver to process signals of the wide frequencyband, wherein the adjacent narrow band signal is located at one of: anedge portion of the wide frequency band; or immediately adjacent to butoutside of the wide frequency band.
 9. The one or moreprocessor-readable memory devices of claim 8, wherein theprocessor-executable instructions are further configured to enable themachine system to: demodulate the narrow band signal; and decode thedemodulated narrow band signal effective to obtain the indicationtherein of whether to wake up the wideband receiver.
 10. The one or moreprocessor-readable memory devices of claim 8, wherein the widebandsignal defines at least one of a Code Division Multiple Access (CDMA)signal and a set of contiguous subcarriers occupying the pre-specifiedwide frequency band defining an Orthogonal Frequency DivisionMultiplexing (OFDM) signal.
 11. The one or more processor-readablememory devices of claim 8, wherein the processor-executable instructionsare further configured to enable the machine system to control a powersupply associated with the wideband receiver effective to wake up thewideband receiver.
 12. The one or more processor-readable memory devicesof claim 8, wherein the processor-executable instructions are furtherconfigured to enable the machine system to stop operation of the narrowband receiver while the wideband receiver is operating.
 13. The one ormore processor-readable memory devices of claim 8, wherein theprocessor-executable instructions are further configured to enable themachine system to periodically wake up the narrow band receiver todetermine if a narrow band signal is being received containing a messagespecific to a wideband receiver associated with the narrow bandreceiver.
 14. A system to control power consumption of a device, thesystem comprising: a wideband receiver implemented, at least in part, inhardware and configured to receive and process a wideband signaloccupying a pre-specified wide frequency band; a narrow band receiverimplemented, at least in part, in hardware, and configured to receive anarrowband signal occupying no more that a narrow band adjacent to anedge of the pre-specified wide frequency band; at least one processor;and one or more processor-readable memory devices comprisingprocessor-executable instructions which, responsive to execution by theat least one processor, are configured to enable the system to: receive,using the narrow band receiver, the narrow band signal, the narrow bandsignal comprising an indication of whether to wake up the widebandreceiver when the wideband receiver is in a non-processing and powersaving mode; process the narrow band signal to determine whether to wakeup the wideband receiver based, at least in part, on the indication; andresponsive to determining to wake up the wideband receiver, wake up thewideband receiver out of the non-processing and power saving modeeffective to process the wideband signal, wherein the narrow band signalis located at one of: an edge portion of the wide frequency band; orimmediately adjacent to but outside of the wide frequency band.
 15. Thesystem of claim 14, wherein the narrow band receiver comprises a passivedevice.
 16. The system of claim 14 further comprising: a power supply;and a switch connecting the power supply to the wideband receiver, theswitch being controlled, at least in part, by the narrow band receivereffective to wake up the wideband receiver.
 17. The system of claim 14,wherein the system is further configured to: demodulate the narrow bandsignal; and decode the demodulated narrow band signal effective todetermine whether to wake up the wideband receiver.
 18. The system ofclaim 14, wherein the system is further configured to periodically wakeup the narrow band receiver.
 19. The system of claim 14, wherein thewideband receiver comprises at least one of: an Orthogonal FrequencyDivision Multiplexing (OFDM) receiver; or a Code Division MultipleAccess (CDMA) receiver.
 20. The system of claim 14, wherein the systemis further configured to process the narrow band signal effective todetermine whether the narrow band signal contains a message specific tothe system.